What is the, "Counterfeit Law" as referenced in Lotus Sutra

In the Lotus Sutra, (Burton Watson translation) there is often mention of "the counterfeit law" being propigated for so-and-so number of small kalpas. I will give an exerpt below, but what exactly is this referring to? I don't know if this is helpful information, but it almost always is talked of in accordance to a prophesy. >"That buddha's life span will be twenty-four small kalpas, his Correct Law will endure in the world for fourty small kalpas, and his Counterfeit Law for fourty small kalpas."